Traditional surgical procedures for pathologies located deep within the body can cause significant trauma to the intervening tissues. These open procedures often require a long incision, extensive muscle stripping, prolonged retraction of tissues, denervation and devascularization of tissue. Most of these surgeries require recovery room time of several hours and several weeks of post-operative recovery time due to the use of general anesthesia and the destruction of tissue during the surgical procedure. In some cases, these invasive procedures lead to permanent scarring and pain that can be more severe than the pain leading to the surgical intervention.
Minimally invasive alternatives such as arthroscopic techniques reduce pain, post-operative recovery time and the destruction of healthy tissue. Orthopedic surgical patients have particularly benefited from minimally invasive surgical techniques. The site of pathology is accessed through portals and cannulas rather than through a significant incision thus preserving the integrity of the intervening tissues. These minimally invasive techniques can often be performed with only a local anesthetic. The avoidance of general anesthesia reduces post-operative recovery time and the risk of complications.
Minimally invasive surgical techniques are particularly desirable for spinal and neurosurgical applications because of the need for access to locations deep within the body and the danger of damage to vital intervening tissues. For example, a common open procedure for disc herniation, laminectomy followed by discectomy requires stripping or dissection of the major muscles of the back to expose the spine. In a posterior approach, tissue including spinal nerves and blood vessels around the dural sac, ligaments and muscle must be retracted to clear a channel from the skin to the disc. These procedures normally take at least one-two hours to perform under general anesthesia and require post-operative recovery periods of at least several weeks. In addition to the long recovery time, the destruction of tissue is a major disadvantage of open spinal procedures. This aspect of open procedures is even more invasive when the discectomy is accompanied by fusion of the adjacent vertebrae. Many patients are reluctant to seek surgery as a solution to pain caused by herniated discs and other spinal conditions because of the severe pain sometimes associated with muscle dissection.
In order to reduce post-operative recovery time and pain associated with spinal and other procedures, micro-surgical techniques have been developed. For example, in micro-surgical discectomies, the disc is accessed by cutting a channel from the surface of the patient's back to the disc through a small incision. An operating microscope or loupe is used to visualize the surgical field. Small diameter micro-surgical instruments are passed through the small incision and between two laminae and into the disc. The intervening tissues are disrupted less because the incision is smaller.
Fusion of the vertebral bodies involves preparation of the exposed endplate surfaces by decortication (scraping the superior and inferior endplates of the cortical bone) and the deposition of additional bone into disc space between the prepared endplate surfaces. Alternatively, other material may be added during fusion such as bone cements or fusion cages. The complete discectomy and fusion may be performed through a posterior surgical route (from the back side of the patient) or an anterior surgical route (from the front side of the patient). The removed vertebral bone may be just the hard cortical bone or may include soft cancellous soft bone in the interior of the vertebral bodies.
Previously used decortication tools had any of a number of flaws. Most of the decortication instruments are of a size that will not allow them to fit into the cannulas that are used to perform non-invasive procedures. Other tools that are small enough in size to be used in non-invasive procedures are unable to decorticate the superior and inferior endplates simultaneously or they require the surgeon to bias its cutting edge against a particular endplate while scraping the adjacent endplate.
Likewise, the tools that are presently available tend to be designed for open surgeries and require a sizeable surgical exposure to be used effectively. In addition, current instruments require the user to bias the shaft of the instrument against one of the endplates (superior or inferior) while simultaneously dragging the cutting edge across the opposite endplate. In this way, the current instruments require the user to use the opposite endplate as a fulcrum to provide adequate leverage to bias the scraping edge of the instrument against the endplate being scraped. Consequently, only one endplate can be decorticated at a time. Due to this limitation in their use, current endplate preparation instruments are not ideally suited for a percutaneous fusion procedure since the access in this new type of surgery is through a fairly narrow tube, and the ability of the user to bias the instrument against one of the endplates is severely limited.
A surgical instrument that is able to decorticate adjacent endplates at the same time will greatly reduce surgical time. An apparatus that is able to decorticate two adjacent endplates at the same time will often reduce the decortication time by more than half as the surgeon is no longer required to bias the instrument against one endplate while scraping the other, invert the instrument, bias it against the other endplate, and scrape the other endplate. Thus, an instrument that can pass easily through a cannula, can decorticate adjacent endplates simultaneously, biases the instrument equally against the two adjacent endplates and will allow decortication to occur evenly with limited scraping time would be highly desired.